1. Field of the Invention
This invention relates to a method and apparatus for sorting coins utilized in automatic vending machines, money exchange machines; service devices, etc., and more particularly to an electronic coin sorting apparatus which sorts coins by electronic means.
2. Description of the Related Art
There have been used two types of coin sorting apparatus. The first type is mechanical sorting apparatus in which the characteristics of coins are mechanically examined or judged for sorting, and the other type is electrical sorting apparatus in which the characteristics of the coins are detected by electronic means and the coins are sorted according to the detected outputs. Since the electronic coin sorting apparatus has a high sorting accuracy and can be miniaturized, this type of the sorting apparatus have been used widely.
An electronic coin sorting apparatus is generally constructed such that a primary coil excited by a signal of a definite frequency is disposed on one side of a coin passage, a secondary coil electromagnetically coupled with the primary coil is disposed on the other side of the coin passage, an attenuating voltage signal generated by the secondary coil which is generated at the time of passing the coin is used to judge whether the coin is genuine or counterfeit, and the reliability of the coin is examined according to a result of judgment.
An electronic coin sorting apparatus has also been proposed wherein a plurality of pairs of coin detecting coils each comprising a primary oscillation coil and a secondary receiving coil are provided for detecting the material, thickness, external diameter or the like of the coin. Further, according to one method, signals of different frequencies are applied to different primary coils while in another method the primary coil itself acts as an element of an oscillation circuit so as to constitute a self-oscillation circuit. In both methods a plurality of discrete driving circuits or oscillation circuits are provided for exciting respective primary coils.
U.S. Pat. No. 3870137 discloses a coin sorting apparatus wherein at least two electromagnetic fields having different frequencies are provided for judging the characteristics of the coin by the action of these electromagnetic fields. Respective electromagnetic fields have different oscillation circuits to be applied with different check frequencies so as to check whether the diameter and thickness of the coin are included in predetermined ranges by using the interaction between the coin and the different check frequencies. When the coin satisfies the check standard of at least two different frequencies, the coin is judged acceptable.
With the prior art, however, to improve the coin sorting accuracy, it is necessary to use a plurality of oscillation circuits and oscillation coils, so that the number of component parts and hence the manufacturing cost are increased. Moreover, since respective oscillation coils are excited by different frequencies, interference between these coils is liable to occur. To avoid the interference, it is necessary to increase the distance between the coils which lengthens the coin passage.
In the prior art coin sorting apparatus, for example, that described in U.S. Pat. No. 3870137, for the purpose of providing interaction with the coin, a plurality of exciting coils respectively excited by low and high frequencies are used. Consequently where clad coins are to be examined wherein the sheets of nickel and copper are superposed as in 10 cent, 25 cent and 50 cent coins, for the purpose of checking characteristics of respective materials, it is necessary to use a plurality of oscillation circuits and oscillation coils. As a consequence, the sorting circuit also become complicated. Furthermore, for the purpose of judging the material and thickness of the coin, an independent low frequency oscillation circuit and a high frequency oscillation circuit are necessary for obtaining discrete mutual reactions so that the judging means becomes complicated in construction. Moreover, such judging means can be used for only a specific type of coins.